Department of Biomedical Engineering, Amirkabir University of Technology (Tehran Polytechnic), Tehran, Iran.
Department of Mechanical Engineering, Amirkabir University of Technology (Tehran Polytechnic), Tehran, Iran.
Ann Biomed Eng. 2021 Jan;49(1):276-286. doi: 10.1007/s10439-020-02541-w. Epub 2020 Jun 3.
Brain, the most important component of the central nervous system (CNS), is a soft tissue with a complex structure. Understanding the role of brain tissue microstructure in mechanical properties is essential to have a more profound knowledge of how brain development, disease, and injury occur. While many studies have investigated the mechanical behavior of brain tissue under various loading conditions, there has not been a clear explanation for variation reported for material properties of brain tissue. The current study compares the ex-vivo mechanical properties of brain tissue under two loading modes, namely compression and tension, and aims to explain the differences observed by closely examining the microstructure under loading. We tested bovine brain samples under uniaxial tension and compression loading conditions, and fitted hyperelastic material parameters. At 20% strain, we observed that the shear modulus of brain tissue in compression is about 6 times higher than in tension. In addition, we observed that brain tissue exhibited strain-stiffening in compression and strain-softening in tension. In order to investigate the effect of loading modes on the tissue microstructure, we fixed the samples using a novel method that enabled keeping the samples at the loaded stage during the fixation process. Based on the results of histology, we hypothesize that during compressive loading, the strain-stiffening behavior of the tissue could be attributed to glial cell bodies being pushed against surroundings, contacting each other and resisting compression, while during tension, cell connections are detached and the tissue displays softening behavior.
大脑是中枢神经系统（CNS）最重要的组成部分，是一种具有复杂结构的软组织。了解脑组织微观结构在机械性能中的作用对于更深入地了解大脑发育、疾病和损伤的发生机制至关重要。尽管许多研究已经调查了脑组织在各种加载条件下的力学行为，但对于报道的脑组织材料性能的变化还没有明确的解释。本研究比较了两种加载模式（压缩和拉伸）下脑组织的离体力学性能，并通过在加载下仔细检查微观结构来解释观察到的差异。我们在单轴拉伸和压缩加载条件下测试了牛脑组织样本，并拟合了超弹性材料参数。在 20%的应变下，我们观察到脑组织在压缩下的剪切模量约为拉伸下的 6 倍。此外，我们观察到脑组织在压缩下表现出应变硬化，在拉伸下表现出应变软化。为了研究加载模式对组织微观结构的影响，我们使用一种新方法固定样本，该方法允许在固定过程中使样本保持在加载阶段。基于组织学的结果，我们假设在压缩加载下，组织的应变硬化行为可能归因于神经胶质细胞体被推向周围环境，彼此接触并抵抗压缩，而在拉伸时，细胞连接断开，组织呈现软化行为。
